Field of the Invention
The invention relates generally to apparatus and methods for locating buried pipes, and more particularly to non-invasive apparatus and methods for locating non-metallic pipes.
Description of Related Art
Pipes may be used to transfer liquid and gaseous substances such as natural gas, water, sewer and liquid petroleum to name but a few. Often, these pipes are buried underground, usually at a depth below the local frost lines. Once buried, the pipes may be difficult locate in the future when needed for service, damage avoidance, leak detection, future continuation of the line, or other purpose. Prior to the 1960's, most such buried pipes were made of metals, clay or concrete. Electromagnetic devices and techniques are commonly used with great effectiveness and precision to locate buried metallic pipes. However, non-metallic pipes, like clay or concrete, were not locatable by traditional electromagnetic means.
In the 1960's the first plastic pipes were installed in large numbers by gas, water, and sewer companies. Plastic pipes, like the earlier clay and concrete pipes, are not locatable by traditional electromagnetic means. Naturally, there have been numerous attempts to find a reliable and repeatable method for locating non-conductive, non-metallic pipe. Unfortunately, available technologies have all fallen short of providing reliable, repeatable locating results, which qualities are required in this field of endeavor. Failure to accurately locate a buried pipe can result in lost work efficiency, property damage, and in some cases can put human lives in danger.
Current systems and methods used to locate buried pipes include Ground Penetrating Radar (GPR). GPR technology has been available commercially for decades. It is a reliable and repeatable technology in certain geographic areas, depending upon the soil type. General estimates suggest that GPR works well in approximately 30% of North America. For example, in sandy soil without rocks or clay deposits, GPR can reliably locate buried non-metallic pipes. However, in clay soils, high water tables, or mixed mediums of rock/clay/loam, GPR is not reliable or repeatable and leaves up to 70% of the subsurface utilities in North America un-locatable.
Magnetometer Locating is technology based on the Electromagnetic Field of the Earth and dependent upon the user's ability and their own personal electromagnetic field. Many professionals attest to the accuracy of these methods. Many more will emphatically state (and Science agrees) there is no basis for this “technology” which is sometimes also categorized with the practices of dowsing and witching.
Technologies are available that either tap or hammer the pipe directly or “hammer” the water in the pipe to cause sound waves. If a technician is hammering the pipe or valve, like the Seba RSP 3 available from Tracer Electronics LLC (Lebanon, Tenn.), the risk of damaging the structure is present, making this a questionable method. If a technician is using a “Water Hammer”, like the Radiodetection RD 500 available from Radiodetection Ltd. (Bristol, UK), the sound waves created are actually pressure changes that can damage pipes. Older pipes and pipe fittings are a high risk with this technology, often causing leaks, dislodging internal corrosion and sediments, along with other potential risks. Another drawback to these methods is the ability of the sound being generated to travel significant distances down the pipe from the point of contact and the lack of ability of the sound being generated to penetrate through the earth to be detectable at the surface. The Applicant has observed that if a pipe is buried more than three feet (3 ft.) deep, the soil resistance makes locating the sound very difficult, if not impossible using these technologies.
Yet another approach to locating non-metallic pipe involves the introduction of a conductive wire or transmitter into the pipe. The wire or transmitter can be used to mark the pipe's location using a traditional electromagnetic locator. One example of this technology can be seen in PCT Patent Publication No. WO 9219988 Connel. These methods should not be used to locate potable water, due to rigid EPA rules concerning introducing a foreign object into drinking water. For non-potable water pipes (storm, sanitary, drains, etc.) the rules are not as stringent, but there are other factors that may make this undesirable. One practical drawback is the contamination or soiling of the wire snaked down the length of the pipe. Non-potable water pipes often contain disgusting sediments and residues that readily attach to the wire and must be removed and cleaned by the technician after the procedure is completed. Also, there are fittings and bends in the pipes that may not allow an object or wire to be pushed through or around these barriers. In larger diameter pipes, the wire or transmitter may not be able to push very far along its path due to the wire flexing. Thicker wire or cable will not bend around the fittings. Thin wire is almost impossible to push any appreciable distance in a large diameter pipe or conduit.
Two more recent technologies include the Inspector 007 from SubSurface Instruments (De Pere, Wis.) and the APL from Sensit Technologies (Valparaiso, Ind.). The Applicant has observed that these technologies tend to register unacceptably high instances of false positives. Hence, these newer technologies must be categorized as not sufficiently repeatable/reliable.
U.S. Pat. No. 4,911,012 to Ziska describes a method for locating underground pipes using vibrations introduced by hammering on an exposed portion of the pipe. A down-range sound detector is used to listen for the vibrations. A significant problem with this type of technique is the loss of signal strength. The down-range detector must be very sensitive to pick-up a signal, and is thus highly susceptible to false-positive indicators emanating from non-relevant sources. Also, because of the loss of signal strength issues, this technique is limited to relatively short-range use.
FIG. 1 is a highly simplified schematic view portraying a prior art method for locating buried pipes P by attaching a vibration transmitter T to an accessible region of the pipe P, and then attempting to listen for emitted vibrations with a receiver R at a downrange sampling location.
Accordingly, none of the currently available technologies and methods are able to locate buried non-metallic pipes with repeatable and reliable results. The failure to correctly locate a buried non-metallic pipe can pose serious risk to people and property, not to mention waste valuable time and work resources. For example, the failure to correctly locate a non-metallic pipe carrying a flammable gas can result in an explosion. The failure to correctly locate a buried non-metallic pipe carrying potable water can result in contamination to drinking water. There is therefore a need in the art for non-invasive systems and methods to repeatably and reliably locate buried non-conductive pipes, using relatively low-cost and easily transported equipment, in a time-efficient manner.